The separation of many classes of compounds by selective adsorption on molecular sieves or zeolites as well as other adsorbents is well known. For example, as disclosed in U.S. Pat. No. 4,048,205, methyl esters of fatty acids of various degrees of unsaturation may be separated from mixtures of esters of saturated and unsaturated fatty acids with X or Y zeolites exchanged with a selected cation. Further in U.S. Pat. No. 4,353,838 it is disclosed that monoethanoid fatty acids may be separated from diethanoid fatty acids with crosslinked polystyrenes, e.g. "Amberlite". The refining of oils by admixing them with magnesium silicate to adsorb coloring matter and free fatty acids from glyceride oils is disclosed in U.S. Pat. No. 2,639,289. Subsequently, it has been suggested in U.S. Pat. No. 2,771,480 to use ion-exchange resins to adsorb the impurities found in glyceride oils. In an article by J. L. Lopez Ruiz et al., Grasas Y. Aceites 25 (5) pp. 280-84 (1974) the separation of monooleins from trioleins by adsorption on a Linde X zeolite (calcium-exchanged X type) was disclosed with desorption by ethyl alcohol. This has the disadvantage that ethyl alcohol can cause transesterification of the triglycerides to form mono- and diglycerides and fatty acid ethyl esters.
The process of separating monoglycerides from di- and triglycerides described herein has many potential uses, for example, the purification of triglycerides, e.g. palm oil, by crystallization, is affected by the presence of monoglycerides. A process which separates monoglycerides from triglycerides can improve the purity and recovery of such crystallizations. Another application of our separation process results from the use of mono- and diglycerides as emulsifiers in large amounts in the food industry. These compounds are produced in ways, i.e., the reaction of glycerol with a fatty acid such as stearic acid, or with triglyceride mixtures such as tallow, which results in a mixture of 1- and 2-monoglycerides, 1,2-diglycerides and 1,3-diglycerides. Separation of the components of the mixture is currently accomplished by molecular distillation, a process requiring high temperatures and high vacuum and which, nevertheless, results in low purities and yields. Applicant's discovery provides real benefits in terms of energy savings and product purity and recovery.
Another important application of our separation process resides in the utility of the separated products, that is, pure monoglycerides and diglycerides, in the synthesis of triglycerides. Cocoa butter, for example, is a high value natural product consisting predominantly of a mixture of particular triglycerides where the 2-position of glycerol is esterified with an oleyl group and the 1- and 3-positions are esterified with either the palmitoyl or the stearyl group. When the 1- and 3-positions are esterified with palmitoyl groups, the triglyceride is referred to as "POP". Likewise, when a stearyl group occupies both 1- and 3-positions, the compound is called "SOS", and when 1- and 3-positions are filled by one palmitoyl and one stearyl group, the compound is referred to as "SOP". Cocoa butter is a predominant component in chocolate confections. It is believed that large quantities of these particular triglycerides could be synthesized and used as cocoa butter extenders. However, it is essential that the oleic acid moiety occurs at the 2-position. This can be assured by using the 2 -oleyl-monoglyceride as precursor for such syntheses. A mixture of 2-monoglycerides and diglycerides can be obtained from the enzyme lipase, which is stereospecific and forms diglycerides and 2-monoglyceride from triglycerides. By reacting lipase with triglycerides containing the 2-oleyl group and separating the resulting mono- and diglycerides a 2-oleyl-monoglyceride could be produced. This separation can be achieved by the invention, whereby the extract will contain the desired 2-monoglyceride. Alternatively, it is possible to synthesize the aforementioned triglycerides by using as precursors 1,3-diglycerides containing palmitoyl and stearyl groups and adding the oleyl group in the 2 position, thereby affording triglycerides such as POP, SOP, and SOS. The process of the instant invention can be used to accomplish this by separation of glyceride mixtures which contain 1,3-diglycerides, obtaining the desired 1,3-diglycerides in the raffinate.
I have discovered combinations of zeolites and desorbents which separate the monoglycerides and diglycerides. The monoglycerides are adsorbed to the substantial exclusion of diglycerides and are concentrated in the extract. The diglycerides, therefore, are removed from the mixture of monoglycerides and diglycerides and are concentrated in the raffinate of the adsorptive separation apparatus.